In the case of OpenBSD itself, the popularity of the PCEngines APU2 has definitely provided motivation for improving the performance of PF.
Also, ironically, people elsewhere in this article thread keep mentioning that older hardware is too power intensive. But the reason the APU2 is still around is because neither Intel nor AMD offer modern chips with a maximum TDP as low as the AMD G series. At maximum load, with all 4 cores, DRAM, and NICs at full throttle, the APU2 only dissipates something like 10W of heat. Modern x86 chips are more power efficient, but their maximum TDPs are just too high. Some of the laptop and embedded series get close at ~15W (not sure if that includes DRAM and NICs), but that's too hot. The APU2 is designed to only require passive cooling, without finned cases, without conditioned air, and still provide years of reliable always-on service.
I see the same issue with higher-end AMD and Intel chips. Under light load their power draw is very low, but under load their chips are often more power hungry than comparable models from 10 years ago. Yes, they get more work done per watt, but there are many situations where I'd rather know that a server will never draw more than, say, 50-60W, even if that means requests end up being throttled. But I don't want to use their crippled low-end chips, either, especially when I can just continue using my 10+ year-old servers that provide better performance. (Theoretically you could manually throttle requests to maintain the power envelope, but I don't want to be burdened managing software configurations.) I prefer the "edge computing" series of chips from Intel and AMD, but over the years their max TDP has slowly crept up. Thankfully there are still a few options that work well, but it's definitely a niche that doesn't see much attention.